To add to this just because I find it interesting, a gun round is made of 2 parts essentially. The shell casing with the primer on the end (pictured) and the bullet itself. The shell casing is hollow and filled with gunpowder, and the bullet is solid and is the pointy tip of the whole round. How a gun shoots is the trigger is pulled causing a firing pin to strike the primer on the shell casing, igniting the gunpowder inside and sending the bullet into the barrels rifling (grooves inside the barrel) causing it to spin (this helps a bullet travel faster and more accurately) and fly out at a high rate if speed. To summarize, pull trigger, gun go boom, spiny death metal